1. Field of the Invention
The present invention relates to an insert film used for forming a resin panel, a process for producing the insert film and a resin panel using the insert film. More particularly, it relates to an insert film having provided therein a printed part.
2. Description of the Related Art
Conventionally, glass is used as a material for a window member of automobiles. However, glass has high specific gravity. Therefore, to attempt making the window material lightweight, a resin window using a resin such as polycarbonates or acrylic resins as a material thereof in place of glass is also used. For example, Japanese Patent Application Laid-Open No. 6-170883 discloses that, because a resin window has a softer surface as compared with a glass window, insert molding is conducted for integral molding by injecting a molten resin in a mold in a state such that a resin (polycarbonate) film or sheet in which one side has been subjected to a hard coat treatment is arranged in an injection molding mold with the hard coat side facing a mold wall, thereby a resin window having a hard coat layer formed on at least one side thereof.
Further, an opaque trimming part (blackout) for playing a role of hiding a mounting portion of a body panel or a printed part for forming a sunshade or the like is sometimes arranged on a resin window. FIG. 6 is a perspective view of a resin window 32 provided with a trimming part as a printed part 31, and FIG. 7 is a partially sectional view thereof. As shown in FIG. 7, the printed part 31 is formed in a state so that it is sealed with a molding resin portion 33 and a resin film or sheet 34 (hereinafter referred to as “resin film 34” for simplicity). In FIG. 6, the printed part 31 is actually in a state that the entire part is completely coated with an ink of dark color, such as black.
In the case of producing such a resin window 32, the resin film 34 in which the printed part 31 is formed by an ink on the side opposite the side to which a hard coat treatment has been applied, is arranged in a fixed mold such that the printed part 31 faces a movable mold. After the movable mold is moved to close the mold, a molten resin is injected into the mold from a gate, thereby integrally molding with the resin film 34.
However, the ink has poor adhesiveness with a polycarbonate, which is a material of the resin film 34. Moreover, in order to attempt to not leave molding trace on an exposed surface of the resin window, if a gate for injecting a molten resin in a cavity of the mold is arranged at one edge side, the printed part 31 at the side near the gate receives great shear force from a molten resin of high temperature and high pressure. As a result, there is the possibility that the surface of the printed part 31 is shaved off and flows away, or a part of the printed part 31 lifts from the resin film 34 and moves, and an ink flow 35 occurs as shown in FIG. 8 resulting in a defective product.
Further, there are the same problems, not limited to just the resin window, in the case where the desired pattern is formed on the surface of a resin panel by integrally molding an insert film or sheet having a printed part on the surface of a molten injection molded resin.
Japanese Patent Application Laid-Open No. 6-270188 discloses a method of solving this problem. That is, in a process for producing a molded product having a pattern thereon, by mounting a sheet having a character or pattern formed thereon on at least one side of a mold cavity such that the character- or pattern-processed surface faces the cavity side, and injecting a thermoplastic resin in the cavity, thereby integrally molding those, pressure and speed of a resin to be injected are controlled to prevent ink flow.
Further, Japanese Patent Application Laid-Open No. 7-308936 discloses that in producing a molded product having a pattern thereon by mounting a resin sheet or film (insert film) having formed thereon a pattern by a printing ink in a mold and injecting a molten thermoplastic resin in the mold, thereby integrally molding those, the sheet or film that the pattern formed by a printing ink is further coated with a saturated thermoplastic polyester resin is used as the insert film, or a saturated thermoplastic polyester resin is contained in the printing ink.
However, in the case that the ink flow is prevented by controlling pressure and speed of the resin to be injected, as disclosed in Japanese Patent Application Laid-Open No. 6-270188, it is necessary to set proper conditions according to a shape and a size of a resin panel, and also there is the problem that a gate shape or a cavity depth of a mold is restrictive.
Further, adhesive force between a pattern and a molding material injected can be improved by covering a surface of a pattern (printed part) with a saturated thermoplastic polyester resin, or mixing a saturated thermoplastic polyester resin in a ink.
However, even if the surface of a pattern (printed part) is covered with a saturated thermoplastic polyester resin, adhesiveness between the ink and the insert film is poor. As a result, when receiving a large shear force in injecting a molding material, it is difficult to prevent ink flow due to lifting of a part of the printed part. Further, if a saturated thermoplastic polyester resin is contained in an ink, it results in diluting the ink. As a result, light transmission rate is not sufficiently suppressed by such a thickness obtained by a general printing method. On the other hand, if an amount of carbon or pigment in an ink is increased to thicken the ink, there is the problem that inconveniences tend to occur in printing.